NCP1200

a compact switching power supply

In designing a product that is powered from the mains, there are various factors that ultimately determine the choice of power supply. Increasingly more manufacturers are choosing a switching power supply, in part because of its light weight and high degree of flexibility.Switching power supplies are often designed to have a ‘universal’ input, such that they can be directly connected to any desired input voltage (normally an ac voltage between 90 and 260 V). With a traditional solution using a transformer, different taps on the transformer would have to be selected to handle this range of input voltages. However, the less experienced among us are often put off by the idea of a regulated power supply, since it suggests complex circuitry that can generate quite a lot of smoke under the right circumstances!Fortunately, semiconductor manufacturers regularly introduce new chips that make it easy for most power supply designers to master the technology. ON Semiconductor have made a significant advance in this area with the NCP1200, which has the advantage that most of the functions are integrated into a single chip, while at the same time the designer is given a certain degree of freedom (in choosing the MOSFET and controlling its conductance, for instance). This article describes how this new chip functions, based on the example of the construction of a complete 12 V / 10 W mains power supply with very low quiescent current.

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